﻿// All of this was taken from http://snipplr.com/view/48906/ and then modified to be an instantiated class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.IO;
using System.Configuration;

namespace GooglePageRankChecker
{
    public class GooglePageRank
    {
        /// <summary>
        /// GoogleChecksum helper method
        /// </summary>
        private void Mix(ref uint a, ref uint b, ref uint c)
        {
            a -= b;
            a -= c;
            a ^= c >> 13;
            b -= c;
            b -= a;
            b ^= a << 8;
            c -= a;
            c -= b;
            c ^= b >> 13;
            a -= b;
            a -= c;
            a ^= c >> 12;
            b -= c;
            b -= a;
            b ^= a << 16;
            c -= a;
            c -= b;
            c ^= b >> 5;
            a -= b;
            a -= c;
            a ^= c >> 3;
            b -= c;
            b -= a;
            b ^= a << 10;
            c -= a;
            c -= b;
            c ^= b >> 15;
        }

        /// <summary>
        /// Computes the checksum value required by Google
        /// </summary>
        /// <param name="url">URL to determine the checksum for</param>
        /// <returns>string containing the value of the checksum</returns>
        private string GoogleChecksum(string url)
        {
            uint GoogleMagic = 0xE6359A60;

            uint a, b;
            uint c = GoogleMagic;

            a = b = 0x9E3779B9;

            int k = 0;
            int length = url.Length;

            // Algorithm
            while (length >= 12)
            {
                a += (uint)(url[k + 0] + (url[k + 1] << 8) + (url[k + 2] << 16) + (url[k + 3] << 24));
                b += (uint)(url[k + 4] + (url[k + 5] << 8) + (url[k + 6] << 16) + (url[k + 7] << 24));
                c += (uint)(url[k + 8] + (url[k + 9] << 8) + (url[k + 10] << 16) + (url[k + 11] << 24));

                Mix(ref a, ref b, ref c);

                k += 12;
                length -= 12;
            }

            c += (uint)url.Length;

            // All cases fall through
            switch (length)
            {
                case 11:
                    c += (uint)(url[k + 10] << 24);
                    goto case 10; // Fall through
                case 10:
                    c += (uint)(url[k + 9] << 16);
                    goto case 9;
                case 9:
                    c += (uint)(url[k + 8] << 8);
                    goto case 8;
                case 8:
                    b += (uint)(url[k + 7] << 24);
                    goto case 7;
                case 7:
                    b += (uint)(url[k + 6] << 16);
                    goto case 6;
                case 6:
                    b += (uint)(url[k + 5] << 8);
                    goto case 5;
                case 5:
                    b += (uint)(url[k + 4]);
                    goto case 4;
                case 4:
                    a += (uint)(url[k + 3] << 24);
                    goto case 3;
                case 3:
                    a += (uint)(url[k + 2] << 16);
                    goto case 2;
                case 2:
                    a += (uint)(url[k + 1] << 8);
                    goto case 1;
                case 1:
                    a += (uint)(url[k + 0]);
                    break;
                default:
                    break;
            }

            Mix(ref a, ref b, ref c);

            return string.Format("6{0}", c);
        }

        /// <summary>
        /// Returns the PageRank of the given URL. Return values are 0 through 10 or
        /// -1 (N/A), which indicates there was an error or the URL is not in the
        /// Google index.
        /// </summary>
        /// <param name="url">URL to test</param>
        /// <returns>int value indicating the Page Rank</returns>
        public int GetPageRank(string url)
        {
            // Calculate URL checksum
            string checkSum = GoogleChecksum("info:" + url);
            string file = string.Format(ConfigurationManager.AppSettings["PageRankCheckURL"], checkSum, url);

            try
            {
                string data = string.Empty;

                // Request PR from Google
                WebRequest request = WebRequest.Create(file);
                using (WebResponse response = request.GetResponse())
                {
                    
                    using (StreamReader reader = new StreamReader(response.GetResponseStream()))
                    {
                        data = reader.ReadToEnd();
                    }
                }

                // Parse PR from string
                int pageRank = -1;
                if (data.IndexOf(':') != -1)
                {
                    data = data.Substring(data.LastIndexOf(':') + 1);
                }

                int.TryParse(data, out pageRank);

                return pageRank;
            }
            catch (Exception)
            {
                return -1;
            }
        }
    }
}
